Optical glass with a high refractive index and a high dispersing ability

ABSTRACT

A TeO2-WO3 glass with a high refractive index Eta d of not lower than 2.0 and a high dispersing ability represented by Abbe&#39;&#39;s number of 21 or less, and having a greatly improved stability with respect to both devitrification and chemical durability, can be obtained by the inclusion, in the composition of the glass, of Li2O and at least one other oxide selected from the group consisting of K2O, MgO, BaO, ZnO, CdO, TiO2, PbO, La2O3, B2O3, Nb2O5 and Bi2O3.

United States Patent Izumitani et al.

OPTICAL GLASS WITH A HIGH REFRACTIVE INDEX AND A HIGH DISPERSING ABILITYTetsuro Izumitani; Kazuo Namiki, both of Tokyo, Japan Hoya Glass Works,Limited, Tokyo, Japan Nov. 3, 1969 Inventors:

Assignee:

Filed:

Appl. No.:

Foreign Application Priority Data I Nov. 20, 1968 Japan ..43/851 18 U.S.CL... 106/47 Q, 106/47 R Int. Cl. ..C03c 3/00, C030 3/12, C03c 3/30Field of Search 106/47 Q, 47 R May 9, 1972 References Cited UNITEDSTATES PATENTS 3,291,620 12/ 1966 Eustropjeu et al 106/47 FOREIGNPATENTS OR APPLICATIONS 736,073 8/1955 Great Britain ..106/47 PrimaryExaminer-Tobias E. Levow Assistant Examiner-M. Bell AttorneyCushman,Darby & Cushman [57] ABSTRACT 2 Claims, No Drawings OPTICAL GLASS WITH AHIGH REFRACTIVE INDEX v AND A HIGH DISPERSING ABILITY The presentinvention concerns an optical glass and, more particularly, it relatesto the glass having a high refractive index -r;d of not lower than 2.0,a high dispersing ability id, of not greater than 21 as expressed byAbbes number, a high chemical durability and low liquidus temperature.

In order to obtain an optical glass having a high refractive index and ahigh dispersing ability, there has been known the use of TeO as aglass-forming oxide and also known the process for producing an opticalglass by the use of this oxide, as disclosed in Japanese Pat. No.19837/67. However, the conventional tellurite glass which contains BaOand other components had a tendency to devitrify, and this representedpoor stability of the melt.

It is, therefore, an object of the present invention to provide anoptical glass having a high refractive index and a high dispersingability.

Another object of the present invention is to provide an optical glasswhich does not tend to devitrify.

Still another object of the present invention is to provide an opticalglass having an improved water-resistance.

Conventional TeO -WO glass containing BaO and other components tended todevitrify when melted. We have unexpectedly discovered that thedevitrifying tendency of TeO W glass is greatly alleviated by theaddition of Li O. Thus, even the most stable 'reo -wo -sao glass amongthe tellurite system has a liquidus temperature higher than that of theTeO -WO -Li O glass obtained by the addition of Li O according to thepresent invention. As will be noted from the following Table l, aconventional glass sample indicated by Number 1, which is the moststable one among the TeO -WO BaO glasses, showed a liquidus temperatureas high as 595 C., while the three glass samples Nos. 2, 3 and 4prepared according to the present invention showed markedly low liquidustemperatures and were so stable that no crystal formation was observedwhen the melts were held at various temperatures for thirty minutes, andthe last sample showed an even lower liquidus temperature of 405 C.

TABLE 1 (each component is expressed by mol percent) Sample Liquidus No.TeO W0 BaO Li O Temp. (C) l 75.0 20.0 5.0 595 2 55.0 20.0 25.0notdevitrified 3 50.0 25.0 25.0 not- I devitrified Ternary TeO -WO -Li Oglasses are very poor in its resistance to water. However, the additionthereto of an oxide selected from the group consisting of K 0, MgO, BaO,ZnO, CdO, Ti0 PbO, 1.43203, B 0 Nb O and si e, to the glass results in agreat improvement of the resistance of the glass to water withoutinterfering with the stability of the glass with respect todevitnfication, as shown in Table 2.

TABLE 2 Waterresistance Liquidus (weight tempera- Sample loss tureNumber TeOz W03 L120 Additive percent) C.)

55.0 25.0 20. 0 1.04 405 55.0 25. 0 16. 0 K10, 4.0 0. 62 388 55.0 25.015.0 B20, 5.0 0.42 492 55.0 .25. 0 18.0 MgO, 2.0 0. 74 356 55. 0 25. 013.0 ZnO, 7.0 0. 03 476 55.0 25. 0 18. 0 CdO, 2.0 0.50 403 55. 0 .25. 016.0 TlOz, 4 0 0.70 476 55.0 25. 0 16.0 PbO, 4 0 0. 25 430 55.0 25. 0lti. 0 LflzOa, 4 0 0. 24 417 55.0 25. 0 16.0 B203, 4.0 0.55 403 55.0 25.0 l6. 0 NbzOs, 4 0 0.46 540 55. 0 25. 0 14.0 Bigot, 6 0 0.05

1 Not (lo-vitrified.

Initial weight (gn) Weight after treatment (gin) Initial weight (gt) X2. The proportions of components are expressed in percent by mol. I

As a result, according to the present invention there is provided theoptical glass which has a high chemical stability and a low liquidustemperature. Furthermore, the optical glass has a high refractive index'nd of not lower than 2.0 and a low Abbes number id of not more than 21as shown in the examples given later in this specification.

The typical glass according to the present invention has a composition,as calculated from the batch on the oxide basis, consisting essentiallyof: a basic glass which comprises, in mol percent, 50-65% TeO 20-30% W010 22% U 0; and at least one additive which is an oxide selected fromthe group consisting of2 10% K 0, 1 4% MgO, 1 6% BaO, l 8% ZnO, l 5%CdO, 1.5 6% TiO 0.5 10% PbO, 0.5 5% La O l 6% B 0 1 6% Nb O and 2 8% Bi0 The reasons for these restrictions of the components are as follows. Abatch of glass having the composition consisting of: the basic glasswhose components are such that the range of TeO content is out of 50 65percent, the range of WO;, content is out of 20 30 percent and the rangeof Li O content is smaller than 10 percent; and the additive selectedfrom the aforesaid group but the range of whose content being such thatthe content of K 0 is greaterthan l0rpercent, and/or the content of MgOis greater than 4 percent, and/or the content of 8210 is greater than 6percent, and/or the content of ZnO is greater than 8 percent, and/or thecontent of CdO is greater than 5 percent, and/or the content of TiO isgreater than 6 percent, and/or the content of PbO is greater than l0percent, and/or the content of La O is greater than 5 percent, and/orthe content of B 0 is greater than 6 percent, and/or the content of Nbog is greater than 6 percent, and/or the content of Bi O is greater than8 percent, will undesirably shown a considerably high liquidustemperature resulting in a markedly increased tendency to devitrify. Onthe other hand, if the batch of glass whose composition is such that thecontent of Li O is greater than 22 percent with respect to the basicglass, and if the additive selected from the aforesaid group but rangeof those content is such that the content of K 0 is smaller than 2percent and/or the content of MgO is smaller than 1 percent, and/or thecontent of BaO is smaller than 1 percent, and/or content of ZnO issmaller than 1 percent, and/or the content of CdO is smaller than 1percent, and/or the content of TiO is smaller than 1.5 percent, and/orthe content of PbO is smaller than 0.5 percent, and/or the content of LaO is smaller than 0.5 percent, and/or the content of B 0 is smaller than1 percent, and/or the content of Nb 0 is smaller than 1 percent, and/orthe content of Bi O is smaller than 2 percent, such a glass isundesirably shows a markedly poor water-resistance.

Some of the examples of the present invention will be given in thefollowing Table 3.

Each glass-forming batch containing a mixture of com ponents having theproportions, on the oxide basis, as shown in the following Table 3 wasmelted in a gold crucible of an electric furnace at a temperature of 800900 C. while stirring with a gold rod. After degassing and homogenizingthe melt, the temperature of the melt was lowered to about 500 C.whereupon, the melt was poured into a mold made of cast iron, followedby annealing and subsequent cooling of the same to room temperature. Theresulting glass was determined as to its refractive index and dispersingability. The results are shown in Table 3.

consisting of2 10% K 0, l 4% MgO, l 6% BaO, l 8% ZnO, l CdO, 1.5 6% 0,0,0.5 10% PhD, 0.5 5%

TABLE 3 Sample Number T002 W0 L120 K MgO BaO B20 PbO Znl.) CdO LazO;NbzO; B1203 T102 nd (1 55. 0 25.0 16. 0 18. TX 55.0 25.0 12. 0 19. 1555. 0 25.0 18. 0 18. 82 55. 0 25. 0 18. O 18. 86 55. O 25. 0 15. 013.!13 50. 0 28. 0 20.0 19. 60. 0 23. 0 15. O 18. 41 56. 0 25. 0 16. 01S. 6% 55. 0 25. 0 16; 0 18. 51 55. 0 25. 0 14. 0 15. m 55. 0 25. 0 17.0is. 621 55.0 25. 0 13.0 15. l 55. 0 25. 0 18. 0 1S. .5 55.0 25. 0 16.01:. $0 55. 0 25. 0 14. 0 :0. H 55.0 25.0 16. 0 17. 53 55.0 25. 0 16.017. 62 55. 0 25. 0 14. 0 1T. 0T 55. 0 25. 0 18. 0 1s. 00 55.0 25. 0 16.017. 61 55.0 25.0 14.0 17.11 55. 0 24. 0 18. 0 1B. 68 55. 0 23. 0 18. 018. 54 55. 0 .20. 0 18.0 l8. 14 55. 0 23. 0 18.!) 18. 75

As clearly seen from the results shown in the above Table, the glassesaccording to the present invention have specific optical constants suchas refractive index 1 d as high as 2.0 2.2 and Abbe 's number as low as17 21, a great stability with respect to devitrification and a highchemical durability. Furthermore, the glasses of the present inventionare suitable for production on commercial basis.

We claim:

1. An optical glass having a refractive index 17d of not smaller than2.0 and an Abbe 5 Number of not greater than 21 consisting essentially,by me], as calculated from the batch on the oxide basis, of a basicglass prepared with the components 50 65% TeO 20 W0 and 10 22% M 0, andan additive consisting of at least one oxide selected from the group1.21 0 1 6% B 0 1 6% Nb O and 2 8% Bi O 2. A method for improving anoptical glass having a refractive index 11d of not smaller than 2.0 andan Abbes number of not greater than 21 composed mainly, on the oxidebasis by mol, of 50-65% TeO and 20-30% W0; with respect todevitrification and chemical durability, comprisng the inclusion of10-22% Li O in said glass to markedly reduce the devitrifying tendencyof the glass, and inclusion in said glass of at least one oxide selectedfrom the group consisting, on the oxide basis by mol, of 210% K 0, 1-4%MgO, l-6% BaO, l8% ZnO, 1-5% CdO, 1.5-6% TiO,, 0.5-10% PbO, 0.5-5% La ol6 B 0 1-6% Nb O and 2-8% B50. to markedly improve the chemicaldurability of said glass.

2. A method for improving an optical glass having a refractive index etad of not smaller than 2.0 and an Abbe''s number of not greater than 21composed mainly, on the oxide basis by mol, of 50-65% TeO2 and 20-30%WO3 with respect to devitrification and chemical durability, comprisingthe inclusion of 10-22% Li2O in said glass to markedly reduce thedevitrifying tendency of the glass, and inclusion in said glass of atleast one oxide selected from the group consisting, on the oxide basisby mol, of 2-10% K2O, 1-4% MgO, 1-6% BaO, 1-8% ZnO, 1-5% CdO, 1.5-6%TiO2, 0.5-10% PbO, 0.5-5% La2O3, 1-6 B2O3, 1-6% Nb2O5 and 2-8% Bi2O3 tomarkedly improve the chemical durability of said glass.